Series stacked transistorized ignition system having diodes in series with the bases



W. R. WOOD SERIES STACKED TRANSISTORIZED IGNITION SYSTEM HAVING DIODES IN SERIES WITH THE BASES Filed May 10, 1962 May 18, 1965 INVENTOR. I/VAFFF/V P W000 2%? xi United States Patent 3,184,638 SERIES STACKED TRANSISTGREZED IGNITION ilissiEiM HAVING DIODES IN SERIES WITH THE Warren R. Wood, Palo Alto, Calif., assiguor to Robert Bosch G.rn.h.H., Stuttgart, Germany Filed May 10, 1962, Ser. No. 193,765 4 Claims. (Cl. 315-206) This invention relates to an improved ignition system for internal combustion engines using spark plugs.

In a typical ignition system, distributor points are opened and closed to pulse current through the primary winding of an ignition transformer. The pulsating current in the primary Winding induces a large voltage in a secondary winding which is connected to one or more spark plugs to produce sparks that ignite a combustible gas mixture in the engine.

One disadvantage of the conventional system is that the distributor points carry the full current flowing through the primary winding, and are subjected to severe arcing as the points open and close. Another disadvantage of the conventional system is that the voltage produced in the secondary winding of the ignition transformer tends to decrease with increasing engine speed.

This invention provides a transistorized ignition system in which the distributor points carry substantially less current than the conventional system, and therefore have longer life due to less severe arcing. Moreover, the secondary winding voltage does not drop oli as fast with increasing engine speed.

Briefly, the improved ignition system of this invention includes a source of electrical power, such as a DC. battery. The system also includes an ignition transformer having a primary winding and a secondary winding. Means are provided for connecting the secondary winding to one or more spark plugs. A plurality of transistors each having a base, emitter, and collector are connected in series so that the emitter of one is connected to the collector of an adjacent transistor. Means connect the transistors in series with the source of electrical power and the primary winding so the transistor controls the flow of current through the primary winding. Biasing means for the transistors are connected in circuit with the source of power and distributor points to apply a pulsating bias voltage to the transistors and thereby control the flow of current through them.

To insure equal voltage across the transistors, the system preferably includes a separate voltage divider resistor connected between the emitter and collector of each transistor.

In the presently preferred system the biasing means include a separate biasing resistor connected across the base and emitter of each transistor. Preferably, a separate diode is connected in series with the base of each transistor and the distributor points to isolate the transistors when the points open. The preferred system also includes separate dropping resistors connected in series with at least some of the bases of the transistors and decreasing in value in the direction in which current flows when the transistors are conducting.

These and other aspects of the invention will be more fully understood from the following detailed description and the accompanying drawing, which is a schematic circuit diagram showing an ignition system embodying this invention.

Referring to the drawing, a source of electrical power 10, say a DC. storage battery, has its negative terminal 12 connected to ground, and its positive terminal 14 connected in series with an ignition switch 16, a ballast resistor 17, and one end of a primary winding 18 of an ignition transformer 20. First, second, and third transistors 3,134,638 Patented May 18, 1965 ice 21, 2.2, and 23, respectively, each having an emitter 24, a collector 26, and a base 27, are connected in series so that their adjacent collectors and emitters are connected together. The emitter of the first transistor 21 is connected through a lead 3% to the end of the primary winding is opposite from the end to which the positive terminal of the battery is connected. The collector of the third transistor 23 is connected to ground.

A separate biasing resistor 32 is provided for each transistor. One end of each biasing resistor 32 is connected to a respective emitter, and the other end of each biasing resistor is connected to the anode of a separate diode 34 provided for each transistor. A first dropping resistor 35 connects the base of the first transistor to the anode of its respective diode. A second dropping resistor 36 connects the base of the second transistor to the anode of its respective diode. The base of the third transistor is connected directly to the anode of its respective diode, and does not require a dropping resistor to limit base current because there is enough emitter-collector voltage drop in the first and second transistors to limit the base current in the tlnrd transistor. Due to the emittercollector voltage drop in the first transistor, the second dropping resistor is smaller than the first. The cathodes of the diodes are each connected to a lead 37, which terminates in a distributor point contact 38. A movable armature 39 is secured by a pivot pin 40 to a lead 41 connected to ground. A compression spring 42 urges armature 39 away from the distributor point contact 38, and against a multi-pointed cam 44 which is driven by the cam shaft of the engine (not shown) to periodically connect distributor point contact 38 to ground. Thus the armature and contact 38 serve as distributor points.

A separate voltage dividing resistor 46 is connected across the emitter and collector of each transistor so that three resistors id are connected in series and serve as a voltage divider circuit across the transistors to insure that voltage is equally divided over them. A capacitor 48 is connected across the emitter of the first transistor and the collector of the third transistor.

A secondary winding 50 of the ignition transformer is connected across one or more conventional spark plugs 51.

A resistor 52 is connected in parallel with the ballast resistor 17 to compensate for the additional voltage drop added to the system by the series connected transistors.

In operating the circuit, the ignition switch 16 is closed, and the engine is started so that cam 44 is rotated to close periodically the circuit between the armature 39 and the distributor point 38.

Each time the distributor point circuit is closed, the transistors are biased on, thereby causing a relatively large current to flow through the primary coil. The current flowing through the distributor point circuit is much smaller because of the amplification provided by the transistors. Due to the relatively large inductance of the primary winding, the current builds up in it relatively slowly. When the distributor circuit opens, the current through the primary winding is suddenly interrupted and the magnetic flux in the ignition transformer is quickly collapsed. This induces a large voltage in the secondary Winding Si and causes a spark across the gap in the spark plug.

As the distributor circuit opens, bias is removed from the transistors and they quickly turn off. Minority carriers in each base flow back to their respective emitters through the biasing resistors. The dropping resistors in series with the bases of the first and second resistors prevent excessive base current flow. However, the third transistor does not need a dropping resistor because there is enough emitter-collector voltage drop in the first and second transistors to limit the base current in it. The

diodes in series with the bases of the transistors isolate the transistors when the distributor points open.

Since the peak voltage in the primary winding of the ignition transformer is ordinarily greater than the avalanche or breakdown voltage of a single transistor that is equally feasible to use in a transistorized ignition system, the plurality of transistors are connected in series. The voltage divider resistors connected between the emitter and collector of each transistor insure that the voltage is equally divided among the transistors, and thus decreases the likelihood that any one of the transistors will fail due to excessive power dissipation by avalanche breakdown. The voltage divider resistors also decrease turn oif time for the transistors. Although not entirely critical, I have found that a satisfactory circuit is produced by using components having the values indicated in the following table:

Table Capacitor 48 0.25 microfarad. Resistors 46 1K ohm each. Resistors 32 10 ohms each. Resistor 35 1.8 ohms. Resistor 36 1 ohm. Resistor 17 1 ohm. Resistor 52 4 ohms.

I claim:

1. An improved ignition system for an internal combustion engine having spark plugs and distributor points for opening and closing a circuit in synchronization with engine operation, the system comprising a source of electrical power, an ignition transformer having a primary winding and a secondary winding, means connecting the secondary winding to the spark plugs, a plurality of transistors each having a base, emitter and collector and an emitter-base path, means connecting the transistors in series so the emitter of one is connected to the collector of an adjacent transistor, means connecting the transistors in series with the source of electrical power and the primary winding so the transistors control the flow of current through the primary Winding, a separate biasing resistor connected across the base and emitter of each transistor, means connecting the biasing resistors in circuit with the source of power and distributor points to apply a pulsating voltage across the biasing resistors and control the flow of current through the transistors, a separate diode connected to and in series with the base of each transistor and the distributor points to isolate the transistors when the points open, and a separate dropping resistor connected in series with the base of each transistor between said base and the corresponding diode to limit base current flow, each of said biasing resistors and each of the corresponding ones of said dropping resistors being connected in series circuit with each other and with the corresponding emitter-base path to form a closed loop comprising a biasing resistor, a dropping resistor and the emitter-base path for each of said transistors.

2. An improved ignition system for an internal C0111- bustion engine having spark plugs and distributor points for opening and closing a circuit in synchronization with engine operation, the system comprising a source of electrical power, an ignition transformer having a primary winding and a secondary winding, means connecting the secondary winding to the spark plugs, a plurality of transistors each having a base, emitter and collector and an emitter-base path, means connecting the transistors in series so the emitter of one is connected to the collector of an adjacent transistor, means connecting the transistors in series with the source of electrical power and the primary Winding so the transistors control the flow of current through the primary winding, a separate biasing resistor connected across the base and emitter of each transistor, means connecting the biasing resistors in circuit with the source of power and distributor points to apply a pulsating voltage across the biasing resistors and control the flow of current through the transistors, and a separate dropping resistor connected to and in series with the base of each transistor to limit base current flow, each of said biasing resistors and each of the corresponding ones of said dropping resistors being connected in series circuit with each other and with the corresponding emitter-base path to form a closed loop comprising a biasing resistor, a dropping resistor and the emitter-base path for each of said transistors.

3. The system according to claim 2 in which the values of the dropping resistors decrease in the direction of current flow through the transistors when they conduct.

4. An ignition system as claimed in claim 2, further comprising capacitor means connected across the series connection of said transistors.

References Cited by the Examiner UNITED STATES PATENTS 3,167,705 1/65 Sohner 315-209 GEORGE N. WESTBY, Primary Examiner.

ARTHUR GAUSS, Examiner. 

1. AN IMPROVED IGNITION SYSTEM FOR AN INTERNAL COMBUSTION ENGINE HAVING SPARK PLUGS AND DISTRIBUTOR POINTS FOR OPENING AND CLOSING A CIRCUIT IN SYNCHRONIZATION WITH ENGINE OPERATION, THE SYSTEM COMPRISING A SOURCE OF ELECTRICAL POWER, AN IGNITION TRANSFORMER HAVING A PRIMARY WINDING AND A SECONDARY WINDING, MEANS CONNECTING THE SECONDARY WINDING TO THE SPARK PLUGS, A PLURALITY OF TRANSISTORS EACH HAVING A BASE, EMITTER AND COLLECTOR AND AN EMITTER-BASE PATH, MEANS CONNECTING THE TRANSISTORS IN SERIES SO THE EMITTER OF ONE IS CONNECTED TO THE COLLECTOR OF AND ADJACENT TRANSISTOR, MEANS CONNECTED THE TRANSISTOR IN SERIES WITH THE SOURCE OF ELECTRICAL POWER AND THE PRIMARY WINDING SO THE TRANSISTORS CONTROL THE FLOW OF CURRENT THROUGH THE PRIMARY WINDING, A SEPARATE BIASING RESISTOR CONNECTED ACROSS THE BASE AND EMITTER OF SAID TRANSISTOR, MEANS CONNECTING THE BIASING RESISTORS IN CIRCUIT WITH THE SOURCE OF POWER AND DISTRIBUTION POINTS TO APPLY A PULSATING VOLTAGE ACROSS THE BIAING RESISTORS AND CONTROL THE FLOW OF CURRENT THROUGH THE TRANSISTOR, A SEPARATE DIODE CONNETED TO AND IN SERIES WITH THE BASE OF EACH TRANSISTOR AND THE DISTRIBUTOR POINTS TO ISOLATE THE TRANSISTORS WHEN THE POINTS OPEN, AND A SEPARATE DROPPING RESISTOR CONNECTED IN SERIES WITH THE BASE OF EACH TRANSISTOR BETWEEN SAID BASE AND THE CORRESPONDING DIODE TO LIMIT BASE CURRENT FLOW, EACH OF SAID BISING RESISTORS AND EACH OF THE CORRESPONDING ONES OF SAID DROPPING RESISTORS BEING CONNECTED IN SERIES CIRCUIT WITH EACH OTHER AND WITH THE CORRESPONDING EMITTER-BASE PATH TO FORM A CLOSED LOOP COMPRISING A BIASING RESISTOR, A DROPPING RESISTOR AND THE EMITTER-BASE PATH FOR EACH OF SAID TRANSISTORS. 